Various studies on a technique regarding an electronic device such as a portable terminal device have been conducted. For example, Patent Document 1 discloses a technique in which a distance between an antenna mounted in a portable communication device and a head is measured using ultrasonic waves and matching conditions of a matching circuit of the communication device are changed on the basis of the distance. In addition, Patent Documents 2 to 4 disclose a technique regarding a speaker of a portable terminal device.
Patent Document 2 discloses a technique in which a distance from an object imaged by an imaging unit is measured and a sound is constantly located in a predetermined space depending on the distance. In addition, Patent Document 3 discloses a technique in which a distance between an auditor and a speaker is measured and the distance is reflected in a coefficient of a filter using a head-related transfer function (HRTF) modeled as a database. Further, Patent Document 4 discloses a technique regarding a portable terminal device including a plurality of superdirective speakers that output sound signals.